The candidate for this Mentored Quantitative Research Career Development Award was trained as a biomedical engineer and has performed experimental and modeling investigations to understand the principles underlying the regulation of muscle force, as well as technique development for the analysis, interpretation and modeling of the data. The mentoring team includes Dr. W. Zev Rymer, a leader in the fields of clinical neuroscience and rehabilitation engineering, Dr. Elliot Roth, an expert in stroke and spinal cord injury rehabilitation, and Dr. C.J. Heckman who is a foremost researcher of spinal cord circuitry and cellular mechanisms of spasticity. The candidate's long-term career goals are two-fold: to apply her experience with the normal operation of the neuromuscular system, to the understanding of the alterations and adaptations that take place in motor disorders so that better-informed interventions may be developed; and to employ the specific insults to the system associated with such disorders to further the basic understanding of the role and significance of the affected regions and pathways in the healthy operation of the system. The proposed research plan addresses the mechanisms underlying common firing patterns exhibited by human motor units. The first part will characterize the role of various central and peripheral sources in healthy subjects using techniques in which the candidate will receive training from distinguished experts of the field: EEG-EMG coherence analysis to be studied with Drs. Bernie Conway and Jay Rosenberg and TMS application with Dr. Leonardo Cohen. The second part of the project will investigate the joint behavior of motor units in two pathological conditions, stroke and complete spinal cord injury, drawing on the known pathologies to identify the role of various components in the generation of motor unit firing patterns. Dr. Christine Thomas will provide training on data collection procedures suited for spinal cord injured patients. The proposed career development program represents an invaluable contribution to the candidate's career providing her with new tools of investigation as well as a deeper understanding of the relevant neuroscience and rehabilitation issues. The Rehabilitation Institute of Chicago offers a uniquely suited environment for this application in terms of both the scientific and clinical expertise of its staff, and its patient population.